Vmax --units

[Deepa Maheshvare]

Hi,

I would like to ask for some clarification in the units of Vmax.In most of the entries,the units of Vmax is gives as U/mg(eg. entry 2919). Here,mg is mg of enzyme or mg of tissue?

Many thanks for your time and kind consideration

Deepa

[Ulrike Wittig]

Hi Deepa,
in your example the unit refers to mg purified protein.
In general the units for Vmax should refer to the mg of protein in the assay.
If cell extracts or tissues are used or dependent on the purity of the protein in the assay of course different proteins could be included in the weight.

Regards,
Ulrike

[Deepa Maheshvare]

Hi Ulrike,

Thank you so much for the explanation.I would like to ask for one more advice.For the cases in which the units of Vmax is given in per gram dry weight of tissue ,is there a way to convert the quantity into per gram of enzyme?

I have seen models where per gram of tissue is considered equivalent to per ml of tissue.Would this be a right substitution?

Thanks a lot for your kind consideration

Deepa

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[Ulrike Wittig]

Hi Deepa,
it's not correct to just set per gram of tissue equivalent to per ml of tissue. And there is no way to automatically convert per gram of tissue into per gram of enzyme.

regards,
Ulrike

[Matthias König]

Just to add.

it's not correct to just set per gram of tissue equivalent to per ml of tissue.

This is true, but most tissues have a density of close to 1g/ml, so using this conversion factors the numerical values are the same.
and the rates in per_g are ~ the rates in per_ml. 

See for instance adipose tissue density of 0.92 g/ml
http://bionumbers.hms.harvard.edu/bionumber.aspx?&id=111213&ver=0&trm=tissue%20density

density of skeletal muscle 1.06 g/ml
http://bionumbers.hms.harvard.edu/bionumber.aspx?&id=111214&ver=1&trm=tissue%20density

Liver is also around 1.00, so pancreas you are interested in is also in the range.
Best M

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